Addition
Select Sysdate,add_months (sysdate,12) from dual; --plus 1 years
Select Sysdate,add_months (sysdate,1) from dual; --Add January
Select Sysdate,to_char (sysdate+7, ' Yyyy-mm-dd HH24:MI:SS ') from dual; --plus 1 weeks
Select Sysdate,to_char (sysdate+1, ' Yyyy-mm-dd HH24:MI:SS ') from dual; --plus 1 days
Select Sysdate,to_char (sysdate+1/24, ' Yyyy-mm-dd HH24:MI:SS ') from dual; --plus 1 hours
Select Sysdate,to_char (sysdate+1/24/60, ' Yyyy-mm-dd HH24:MI:SS ') from dual; --plus 1 minutes
Select Sysdate,to_char (sysdate+1/24/60/60, ' Yyyy-mm-dd HH24:MI:SS ') from dual; --plus 1 secondsSubtraction
Select Sysdate,add_months (sysdate,-12) from dual; -Minus 1 years
Select Sysdate,add_months (sysdate,-1) from dual; --Minus January
Select Sysdate,to_char (sysdate-7, ' Yyyy-mm-dd HH24:MI:SS ') from dual; -Minus 1 weeks
Select Sysdate,to_char (sysdate-1, ' Yyyy-mm-dd HH24:MI:SS ') from dual; -Minus 1 days
Select Sysdate,to_char (sysdate-1/24, ' Yyyy-mm-dd HH24:MI:SS ') from dual; -Minus 1 hours
Select Sysdate,to_char (sysdate-1/24/60, ' Yyyy-mm-dd HH24:MI:SS ') from dual; -Minus 1 minutes
Select Sysdate,to_char (sysdate-1/24/60/60, ' Yyyy-mm-dd HH24:MI:SS ') from dual; -Minus 1 seconds the date and date cannot be added together with a date and number
Sql> select sysdate+1 from dual; Date and date can be subtracted
Sql> select Sysdate-sysdate from dual;
Add_months (d,x)
Returns the D date plus the date after x months
Last_day (D)
Returns the date of the last day of the month that contains the date D
Add_months (sysdate,1) plus a month
Add_months (sysdate,-1) minus one months
Sysdate+1 plus one day -------------------------------------------------------------------------------
Months_between (D1,D2)
Returns the number of months between D1 and D2
New_time (D,Z1,Z2)
Returns the time in time zone Z1 when D is Z2
Next_day (D,s)
Returns the next day that satisfies the condition s
S is the day of the week
Round (D,F) 
Date D is rounded by format F  
 
Sysdate Returns the current time of the database  
 
Trunc (d,f)  
truncate time by format F D  
In addition: the date can be directly added  
such as:sysdate +1,sysdate -1 ------------------------------------------------------------sysdate+1 plus One day
SYSDATE+1/24 plus 1 hours
SYSDATE+1/(24*60) plus 1 minutes
SYSDATE+1/(24*60*60) plus 1 seconds
Date Plus and minus in Oracle
